In general, a hydraulic excavator that is represented by a construction machine is constituted by an automotive lower traveling structure, an upper revolving structure that is mounted to be capable of revolving on the lower traveling structure and a working mechanism that is liftably provided in a front side of the upper revolving structure. The upper revolving structure is provided with an engine mounted thereon in a rear part of a revolving frame for driving a hydraulic pump, and is provided with a cab, a fuel tank and an operating oil tank thereon in a front side of the revolving frame.
Here, a diesel engine is generally adopted as an engine that is a prime mover of the hydraulic excavator. There are some cases where harmful substances made up of, for example, particulate matter (PM) and nitrogen oxides (NOx) are contained in an exhaust gas that is discharged from this diesel engine. Therefore, the construction machine that is represented by the hydraulic excavator is provided with an exhaust gas purifying apparatus in an exhaust pipe forming an exhaust gas passage of the engine.
This exhaust gas purifying apparatus is provided with a post-treatment device comprising an oxidation catalyst unit (generally called a diesel oxidation catalyst, DOC in short) that oxidizes, for example, nitrogen monoxide (NO), carbon monoxide (CO) and hydrocarbon (HC) contained in an exhaust gas for removal, a particulate matter removing unit (generally called a diesel particulate filter, DPF in short) that is arranged downstream of the diesel oxidation catalyst and traps the particulate matter in the exhaust gas for removal, and the like (Patent Document 1).